<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        table,td{
            border:1px solid #333;
        }
        table{
            width:700px;line-height: 50px;
            border-collapse: collapse;
        }
        /* odd奇数  even偶数 */
        /* tr:nth-child(even){
            height:50px;
        } */
        /* 倍数选择器 */
        tr:nth-child(2n+2){
            height: 50px;
        }
    </style>
</head>

<body>
    <table>
        <tr>
            <td>手机</td>
            <td>手机</td>
        </tr>
        <tr></tr>
        <tr>
            <td>手机</td>
            <td>手机</td>
        </tr>
        <tr>
        </tr>
        <tr>
            <td>手机</td>
            <td>手机</td>
        </tr>
    </table>
</body>

</html>